Sandwich structured poly(vinylidene fluoride)/polyacrylate elastomers with significantly enhanced electric displacement and energy density

While polymer dielectric capacitors are preferred energy-storage components in electrical power systems, the low achievable energy densities (U_e) of existing polymer systems restrict their miniaturization and advanced applications. Here, we report the design and preparation of all-polymer sandwich structured films comprised of two outer layers of poly(vinylidene fluoride) (PVDF) to provide high breakdown strength and an interlayer of acrylic rubber dielectric elastomers (DEs) to offer high electric displacement. The energy storage performance of the sandwich architecture films can be significantly improved by modulating the thickness of DEs, as confirmed by the electric displacement-field (D-E) loops and leakage current measurements. Markedly enhanced electric displacement (D_max-D_r = 11.01 μC cm^-2) and a breakdown strength E_b of 438 MV m^-1 have been achieved in the sandwich structured films with an optimum DE central layer thickness of 4 μm, which leads to an ultrahigh energy storage density of 20.92 J cm^-3 and a high efficiency of 72%, by far the highest values ever achieved in all-polymer dielectrics. Excellent reliability in energy storage performance demonstrated by consecutive cycling is presented in the prepared layered films. The spatial organization of the DE into the sandwich structures provides an effective way for achieving the high energy storage capability for flexible energy storage devices.